1. Field of the Invention
The present invention relates to a printing apparatus and, more particularly, to a printing apparatus that uses a printhead including a heating element (heater) to discharge ink.
2. Description of the Related Art
Some of inkjet printing methods of discharging ink droplets from nozzles and adhering them to a printing medium such as a paper sheet or a plastic film use a printhead including a heater that generates heat energy to discharge ink. For a printhead according to this method, for example, electrothermal transducers, a driving circuit thereof, and the like, can be formed using the same process as a semiconductor manufacturing process. Hence, the printhead has the advantages of facilitating high-density nozzle integration and achieving high-resolution printing.
In this printhead, an ink discharge failure may occur in some or all of the nozzles of the printhead due to nozzle clogging caused by foreign substances or high viscosity ink, bubbles trapped in an ink supply channel or a nozzle, a change in wettability on a nozzle surface, or the like. To avoid degradation of image quality caused by such a discharge failure, it is preferable to quickly execute a recovery operation of recovering the ink discharge state or a complementary operation by another nozzle. However, to quickly perform these operations, it is very important to judge an ink discharge state or a discharge failure occurrence accurately at an appropriate timing.
Hence, there have conventionally been proposed various ink discharge state judgment methods and complementary printing methods and apparatuses using them.
As a printing method of detecting a printed product and obtaining a faultless image, Japanese Patent Laid-Open No. 6-079956 discloses an arrangement for printing a predetermined pattern on a detection paper sheet, causing a reading apparatus to read it, and detecting an abnormal printing element. According to Japanese Patent Laid-Open No. 6-079956, image data that should be used for an abnormal printing element is moved and superimposed on image data to be used by another printing element, and complementary printing is performed to obtain a faultless image.
Japanese Patent Laid-Open No. 3-234636 discloses an arrangement using a full-line printhead corresponding to a printing medium width, in which a detection means (reading head) for detecting whether or not ink has been discharged is provided to uniform the discharge states of nozzles arrayed in the widthwise direction of the printing medium. Japanese Patent Laid-Open No. 3-234636 also discloses an arrangement for setting appropriate control based on a nozzle driving condition at the time of detection.
As a method of detecting ink droplet discharge, Japanese Patent Laid-Open No. 3-194967 discloses an arrangement for causing a detection means including a set of a light-emitting element and a light-receiving element which are arranged at one end and the other end of the nozzle array of a printhead to determine the ink droplet discharge state of each nozzle.
Japanese Patent Laid-Open No. 58-118267 discloses a method of arraying heat conductors at positions affected by heat generated by heaters and detecting a change in the resistance value of each heat conductor, which changes depending on the temperature, that is, performing detection on the ink discharge source side, instead of directly detecting the ink discharge state.
As an arrangement for similarly performing detection on the ink discharge source side, Japanese Patent Laid-Open No. 2-28935 discloses an arrangement in which heaters and temperature detection elements are provided on a single support base (heater board) such as an Si (silicon) substrate. Japanese Patent Laid-Open No. 2-28935 also discloses providing temperature detection elements that have film-like shape and overlap heater array regions. In addition, Japanese Patent Laid-Open No. 2-28935 discloses an arrangement for judging ink discharge failure based on a change in the resistance value of a temperature detection element according to a temperature change. Also described is forming a temperature detection element having film-like shape on a heater board by a film forming process and connecting the temperature detection element to the outside via a terminal by a method such as wire bonding.
In the discharge state judgment method disclosed in Japanese Patent Laid-Open No. 6-079956, however, it is very difficult to quickly judge the discharge state because a nozzle with a discharge failure is detected based on the reading result of a check pattern printed on a paper sheet, assuming that the check pattern is printed prior to the judgment. In addition, a reading apparatus needs to be provided, and accordingly, the printing apparatus becomes bulky and expensive.
In the arrangements disclosed in Japanese Patent Laid-Open Nos. 3-234636 and 3-194967 as well, the apparatus has difficulty in downsizing and cost reduction. It is also difficult to quickly detect a nozzle having discharge failure.
In the arrangements disclosed in Japanese Patent Laid-Open Nos. 58-118267 and 2-28935, the problems of Japanese Patent Laid-Open Nos. 6-079956, 3-234636, and 3-194967 are supposedly relaxed. However, the arrangements are still insufficient for accurately judging the discharge state. Especially, in Japanese Patent Laid-Open No. 2-28935, it is impossible to accurately specify a nozzle with discharge failure.